Direction finding system



April 3, 1951 l.. LIBBY ET A1.

DIRECTION FINDING SYSTEM 2 Sheets-Sheet l Filed Feb. 14, 1946 April 3, 1951 l.. 1 LIBBY ET AL 2,547,028

DIRECTION FINDING SYSTEM Filed Feb. 14, 194e 2 sheets-sheet 2 INVENTORS 5575/? L L/BBY fasi/vf C045 Patented Apr. 3, 1951 UNITED STATES ATENT ortie DIRECTION FINDING SYSTEM Application February 14, 1946, Serial No. 647,603 13 claims'. (c1. 34a-.121)

This invention relates to direction nding system.

An object of the present invention is the provision of an improved direction nding system.

Another object of this invention is the provision of a direction finding system in which no moving parts are employed.

YAnother object of this invention is the provision of a direction iinding system utilizing a stationary antenna system and a cathode ray tube indicating system in which no moving parts are employed.

Another object of the present invention is the provision of a direction iinding system utilizing a.` stationary antenna system and a cathode ray tube in which the rotation of the iield pattern of the antenna system and the rotation of the beam in the cathode ray tube are electronically ellected and in which both such eiiects are controlled by potentials derived from a single source.

Another object of the present invention is the provision of a direction finding system of the type hereinabove described, in which the indcation on the cathode ray tube is in the form of a radially extending narrow line.

Another object of the present invention is the provision of a direction nding system of the type hereinabove described in'which the rotation of the radiation pattern of the antenna system and the rotation ofthe beam in the cathode ray tube are positively synchronized.

While our invention itself is defined in the appended claims, other and further objects thereof will become apparent and the invention will be best understood from the following description of an embodiment thereof, reference being had to the drawings, in which:

Fig. 1 is a schematic and block diagram of a direction finding system embodying our invention; and

Fig. 2 is a schematic and block diagram showing a modification thereof.

Referring now to Fig. 1, directive reception patterns, such as for example. crossed figure-ofeight radiant action patterns -may be produced by any suitable means, such as for example, loop antennas I and 2, which are crossed and arranged at right angles to each other and which operate in conjunction with a sensing antenna V3 to provide an unambiguous sense of direction.

The radiation pattern produced by loop antennas I and 2 may be effectively rotated by means of an electronic goniometer generally designed by the numeral 4, which consists of two balanced modulators 5 and 9 respectively associated with loops I and 2. Balanced modulators 5 and 6 include tubes 'l and 8, and 9 and I0 respectively, which may be for example, pentodes. The ends of loop I are connected to the first grids of tubes 'I and 8, while the ends of loop -2 are connected to the rst grids of tubes 9 and I0. The cathodesof tubes 'I--I are all connected to ground while the anodes of tubes 1-I0 are connected together through a resistor II to the positive side of a source of potential whose negative side is, connected to ground. The second grids of tubes 'I-Ill are connected over lines I3--I6 respectively to a source of modulating or control voltages.

The control voltages are derived from an oscillator I'I which may operate at a relatively low frequency, such as 20 cycles per second, or Whatever frequency it is desired to utilize as the rate of the eiective rotation of the radia tion pattern of loops I and 2. The sinusoidal output of oscillator I1 is fed through a 90 phase shifter I3 to output lines I9 and 20. The potentials on the output lines I9 and 20 with respect to ground are out-of-phase with each other. These 90 out-fof-phase voltages, which are unbalanced with respect to ground, are fed through two transformers 2| andv 22,V `rwhich changes them from an unbalanced to a balanced potential with respect to ground. The outputs of transformers 2I and 22 are fed to lines I3 through I6 respectively. The potentials on lines I3 and I4 are 180 out-of-phase with each other; likewise the potentials on lines I5 and I6 are out-of-phase with each other. But it is to be noted that the potentials on lines I3 and I4 are 90 out-.of-phase with respect to the potentials on lines I5 and I6. Stated another Way and designating the phase of the potential on line I3 as the reference phase, the potential on line I5 lags the reference potential by 90, the potential on line I4 lags the reference potential by 180 and the potential on line I0 lags the reference potential by 270. Thus the phases of the potentials on lines lB-IB follow each other sequentially with 90 phase shift in between in the following order: line I3, line I5, line I4 and line I6.

Referring back to the Velectronic goniometer 4 and to the tubes 1.-,-10 thereof, if loop I is oriented in a north-south direction, tube l vmay be assumed to correspond to the north and tube 8 to the south; While Since loop 2 is therefore orlented in an east-west direction, tube 9 will correspond tothe east and tube Ill will correspond to the'west. [As the control voltagesare applied lrespectively to the grids of tubes 34--3'I.

over line I6 to tubes 'I-I successively reach their peak, it will be seen that tube 'I will first reach its maximum positive potential, then tube 9, then tube 8 and finally tube I9. The effective rotation of the radiant action pattern then will be in a clockwise direction from north to east to south to west. The foregoing is of course dependent upon the sensing antenna 3 to eliminate the usual 180 ambiguity of such pattern. For this purpose, the sensing antenna 3 is connected through an appropriate phase shift coupling arrangement 23 to a pentode amplifier 24 Whose anode 25 is connected also in series with resistor II to the positive side of the source of potential I2. Thus, it will be seen that the output of sense antenna 3 is properly mixed with the output derived from the loops I and 2. yThe resultant output derived across resistor Il is then applied through a suitable coupling condenser 25 to a conventional receiver and detector 2'! whose output, which is sinusoidal in form, is then applied through a coupling condenser 28 and over a line 29 to one end of the grid resistors 39-33 associated with tubes 34 to 3l of an electronic mixer or distributor 38, the other end of said resistors 30-33 being connected to the grids of tubes 34-31. Distributor 38 is used to mix and distribute the energy to the deflection plates 59-42 of a cathode ray tube 43, in synchronism with the rotation of the radiant action pattern of the antenna system, or in synchronism with goniom- For this purpose, lines |3--|9, which carry the control voltage potentials, are coupled Thus, each of the tubes 34-37 successively reaches its -point of maximum conductivity in synchronism with its corresponding one of tubes 1-19 respectively. The anode of tube 34 is connected to the deflecting plate 39 corresponding to a deflection of the beam in a direction designated as north on the screen of cathode ray tube 43, the anode of tube 35 is connected to the south deflection plate 4|, the anode of tube 36 is connected to the east deflection plate 49 and the anode of tube 31 is connected to the west deection plate 42.

The anodes of tubes 34-31 are also each connected through condensers 44-4'! respectively to ground. These condensers store up the charge as the tubes 34-31 respectively reach their maximum conductivity so as to obtain a deflection corresponding to the peak voltage of the incoming signals. This storage system for indicating devices is more fully described in the copending applications of G. S. Burroughs 3, Serial No.

592,401, filed May 7, 1945, now abandoned, and G. S. Burroughs 6, Serial No. 626,129, filed November 1, 1945, now forfeited. v

Assuming that a signal is coming in from the northeast, each time that tubes V54 and 35 conduct, a charge is stored in condensers 44 and 45 respectively, which would tend to deflect the beam in a direction corresponding to the northeast. This deflection, would, in the absence of anything further, be merely a deection of a spot from the center of the screen. In order to change this spot deflection into a linear or line deflection 49 as illustrated, the voltages applied to the accelerating electrodes 49 are derived from an A. C.

source 59 through a transformer 5E and across v a voltage divider 52. The application of alternating current to the acceleration electrodes varies the deflection sensitivity of the beam at the frequency of the current derived from source 59. Consequently, at that frequency the beam moves radially from and back to the center of the put. duced equal to the sums and difference fretube (in a northeasterly direction in the instance hereinabove cited) thus producing the line 48. To assure centering of the beam, the cathodes of tubes 34 and 35 are connected to the opposite ends of the resistors of a potentiometer 53 While the catho-des of tubes 35 and 3l are likewise connected to the opposite ends of the resistors of a potentiometer 54. The arms of potentiometers 53 and 54 are in turn connected to the opposite ends of the resistor of a potentiometer 55 whose arm is connected to ground. By suitably adjusting the arms of potentiometers 53 to 55, the spot can be properly centered.

For proper operation of the system described, it is necessary that each of the balanced modulators 5 and 5 be balanced with respect to the other'and with respect to itself. This may be accomplished by controlling the voltages applied to the screen electrodes of tubes 1 !9. For this purpose, the source of voltage for controlling the bias of the screens may be applied through the secondaries of transformers 2i and 22 and through the lines |9-I6 to the various screen grids. The positive side of source 55 may be connected to an arm of a potentiometer 51 whose resistor is connected at its ends tothe arms of two other potentiometers 58 and 59 respectively. Transformers 2| and 22 both have split se'condaries and since the circuit coupled to these are alike, only the connections from potentiometer 59 to its associated transformer 2| will be described. The two halves 99 and 6| of the split secondary of transformer 2| have their outer ends connected respectively to lines I3 and I4 while their inner ends are each connected to the ends of the resistor of potentiometer 59. The halves and 6| are coupled to each other at the frequencies involved (the frequency of oscillator Il) by two series condensers 62 and 63 respectively, the midpoint between said condensers being connected to ground. By adjusting the arm of potentiometer 59, tubes 'I and 8 are balanced with respect to each other. Likewise by adjusting the arm of potentiometer 58, tubes 9 and I9 are balanced with respect to each other. Finally by adjusting the arm of potentiometer 51, balanced modulator 5 is balanced with respect to balanced modulator 6.

One advantage of the system herein described is that it` is not necessary for the modulator tubes to be selected for their characteristics. Any distortion introduced by the modulators will not substantially affect the bearing indications. It is only necessary to balance the modulators for modulation sensitivity. This is due to the fact that in the process of demodulation, the reference voltages, that is, the voltages derived from oscillator Il, are combined with the receiver out- The result is that new voltages are-proquencies of the applied and reference voltages. Since the frequencies are identical, the difference frequency is zero or direct current. This Will cause a resultant deflection of the indicator. Any new frequencies produced (i. e. sums, etc.) will not change the D. C. level since the condensers 44--41 serve as a short to ground for alternating current.

While in the system illustrated in Fig. l, the demodulator is disclosed as consisting of four triodes, it is possible to'substitute in place thereof four diodes. The use of diodes has the advantage that balancing of the diodes becomes unnecessary, and centering of the spot in the cathode ray tube may be accomplished magnetiassitanceV cally. It is preferred 'to operate the'diodes with large. signals so that their characteristics are essentially linear. 'l'herefore no balancing controls are necessary for the demodulators and the diodes may be changed without affecting the accuracy or calibration of the system. For this purpose, the portion of the system of Fig. 1 to the right of the dotted line Sil-64 may be replaced by the arrangement illustratedin Fig'. 2.

`In Fig. 2, lines I3 and Eli are connected to the anodes of a double diode 65 while lines I5 and f5 are connected to the anodes of a double diode 56. The ycathodes of double diodes 65 and are connected together and through line 2.9 to the output ofthe receiver', with the potential applied to the cathodes being developed across a resistor 67 connected to ground. D. C. returns SS and 69 are associatedwith diodes S5 and 6B reispectivelmeach consisting of a pair of resistors connecting the anodes of its -associated diodes with themidpoint between said resistors connected to ground. The output of diodes 65 and 65 is applied to the deiiection plates of the cathode ray tube 43 through low pass filters 'lil and ll,

each of which is balanced with respect to ground.

The low pass iilters and il eliminate any alternating current output and only permit the D. C-. potentials to be applied to the deflection plates. Y

It is preferred in both embodiments that the output of oscillator Il, as'applied to the demodulators, be very much greater than the output derived from the receiver, and may be for example, twice or several times as large as the output of the receiver. For this purpose, suitable amplifiers (not shown) may be interposed between oscillator'il and the transformers 2i and 22. This makes the frequency of oscillator Il the dominant frequency in the beating phenomena in the demodulators and lessens the possibility ci any other frequency producing a D. C. output.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of our invention.

We claim:

1. A direction finder comprising an antenna system having a plurality of directive radiant action patterns, a plurality of modulators, means for applying energy derived from said antenna system in accordance with each of said patterns to the input of separate ones of said modulators, a source of modulating voltages having a plurality of outputs with each of said outputs being displaced in phase with respect to the others, means for separately applying the outputs from said source to separate ones of said modulators to produce/in eiect an azimuthal shifting of the radiant action patterns, a receiver, means coupling the outputs of said modulators to said receiver, an electronic distributor having a plurality of electron discharge devices, means coupling the output of said receiver to each of said devices in parallel, means applying the outputs from said source to separate ones oi said devices to control the conductivity thereof, a cathode ray tube including a plurality of means for deflecting the beam, each deiiecting the beampin different directions and means for separately applying the outputs from said devices to separate ones of said deflection means.

2. A direction finder according to claim 1 further including a sensing antenna, phase shifting means associated with said sensing antenna land means for coupling the output of said ksensing Y' antennato said receiver.

3. A direction-finder vaccording to claimV v1, wherein said cathode ray tibe includes a plurality of accelerating electrodes, a source of alternating current voltages and means for applying said alternating current voltages to said `accelerating electrodes to produce a cyclically varying change in the deiiection sensitivity of the beam.

4. A direction finder according to claim 1, wherein said antenna system Acomprises a pair of crossed loops providing a pair of crossed fig'- ure-of-eight radiant action patterns.

5. A direction finder according to claim l, wherein said antenna system comprises a pair' of crossed loops providing a pair of crossed figure-of-eight radiant action patterns and said modulators are comprised of two pairs of'bala-nced modulators, each of said balanced modulators being coupled in push-pull to the ends of one of said loops.

6. A direction nnder according to claim 1, wherein said antenna system comprises a pair of crossed loops providing a pair of crossed figureof-eight radiant action patterns and said modulators are comprised of two pairs of balanced modulators, each o'f said balanced modulators being coupled in push-pull to the ends of one of said loops, and said source of modulating voltages comprises means for producing four phases of potential with respect to ground, with each phase being successively displaced y with respect to the preceding phase, and means for applying each of the pairs of resulting potentials of phase displacement in push-pull to separate ones of said balanced modulators to produce in effect a rotation of the radiant action patterns.

7. A direction finder according to claim 1, wherein said plurality of delecting means is cornprised of two pairs of spaced deection plates arranged at right angles to each other', each plate being adapted to produce a deflection of the beam in one radial direction from the center.

8. A direction nder comprising an antenna system having a pair of crossed iigure-of-eight radiant action patterns, a pair of balanced modulators, means for applying energy derived from said antenna system in accordance with each of said patterns in push-pull to the input of separate ones of said modulators, a source of modulating voltages having dual outputs of voltages with one output displaced substantially 90 in phase with respect to the other, and each output having two leads 180 out-of-phase with respect to each other and balanced with respect to ground, means separately applying the outputs from said source in push-pull to separate ones of said balanced modulators to produce in eifect a rotation of the radiant action patterns, a sensing antenna including phase shifting means, a receiver, means coupling the outputs of said modulators and sensing antenna to said receiver, an electronic distributor having four electron discharge devices, means coupling the output of said receiver to each of said devices in parallel, means coupling the leads from said source to separate ones of said devices to control the conductivity thereof, a cathode ray tube including iour deflection plates for deecting the beam in orthogonal coordinates, and means for separately applying the output from said devices to separate ones of said deflection plates.

9. A direction finder according to claim 8,.

wherein said cathode ray tube includes acceleratingelectrodes a source of alternating current voltages, and means for applying said alternating current voltages to said acceleratinggelectrodes to cyclically vary the deflection sensitivity of the beam of said cathode ray tube.

10. A direction nder comprising an antenna system providing a directive radiant action'pattern, a local oscillator, means for modulating the energy derived fromY said antenna system With that derived from said local oscillator, a receiver responsive to the output of said modulator, a mixer for mixing the output of said receiver with energy from said oscillator to thereby produce direct current voltages and alternating current components, means for filtering out said components, a cathode ray tube, and means for applying said direct current voltages to deflect the beam in said tube.

' 11. A direction finder according to claim 10 -wherein said modulating means comprises two pairs of balanced modulators, and means for shifting the phase of oscillations derived from said local oscillator to produce an effective rotation of the directive radiant action pattern.

12. A direction finder according to claim 10 wherein said mixer is comprised of a plurality of diodes, and said filtering means comprises a plurality of low pass lters connected to the outputs of said diodes.

13. A direction nder according to claim 10 wherein said modulating means comprises two pairs of balanced modulators, phasing means for shifting the phase of energy derived from 8 said local oscillator so as to produce potentials of four different phases, eachl substantially90 displaced from each other, and means for applying the output Yof said phasing means to said balanced modulators to produce an eiective rotation of the directive pattern of said antenna system, said mixer being comprised of four diodes, to each of which a separate phase of energy derived from the local oscillator is applied from the output of the phasing means, and means coupling the output of said receiver to saidmixer, the outputs of said local oscillator having a sub stantially larger amplitude than the output of said receiver.

v LESTERL. LIBBY,

EUGENE COLE.

REFERENCES CITED The following references are of record in the le of this patent:

s UNITED STATES PATENTS Date 

